1. Field of the Invention
The present invention relates to an electronic circuit component and more particularly to an improvement in adhesion between a circuit conductive layer and an insulating film disposed in such an electronic circuit component as a multi-layered circuit substrate, including the insulating film made of a high polymer material between layers and the circuit conductive layer made of a superconducting metal.
2. Description of the Related Art
Conventionally, a circuit conductive layer of an electronic circuit component such as a multi-layered circuit substrate on which a Josephson device made of a superconducting material is mounted, is essentially fabricated by the steps of: forming an insulating film made of a polyimide resin with a relatively small dielectric constant of 3 to 3.5 on a substrate made of such a material having an excellent insluating property as alumina, mullite, silicon or the like; forming thereover a circuit conductive layer made of niobium (Nb), which is a superconducting metal, by means of a thin film forming method based on the vapor phase growth technique such as evaporation, sputtering and the like; and forming a very fine circuit pattern by means of the photolithography technique, so that a multi-layered structure of the insulating film and the circuit conductive layer is fabricated. Thus, a multi-layered circuit substrate featuring a high density and a high-level function as well as permitting a high-speed operation of the superconducting Josephson integrated circuit device has been obtained.
However, as an operation speed of the superconducting Josephson device has increased recently, the dielectric constant of 3 to 3.5 and a dielectric loss of about 20.times.10.sup.-5 of the conventional polyimide resin have become so great that it is difficult to accomplish a high-speed transmission of signals and, in turn, it is impossible to perform the high-speed operation in the superconducting Josephson device.
With an aim at eliminating such a drawback of the prior-art multi-layered circuit substrate, studies have been made to obtain a multi-layered circuit substrate featuring the high density and the high-level function as well as permitting the high-speed operation of the superconducting Josephson integrated circuit device. For example, such a multi-layered circuit substrate may be fabricated by the steps of: forming, on a ceramic substrate, an insulating film made of a fluorine-containing polymer or a fluorine-containing cycloaliphatic polymer which have a small dielectric constant of about 2.0 and a small dielectric loss of 7.times.10.sup.-6 ; forming thereon a circuit conductive layer made of the superconducting metal by means of the thin film forming method based on the vapor phase growth technique such as evaporation, sputtering and the like; and forming a very fine circuit pattern by means of the photolithography technique, so that the multi-layered structure of the insulating film and the circuit conductive layer is fabricated.
However, the following problem exists in the multi-layered circuit substrate using the insulating film made of a high polymer material such as the fluorine-containing polymer or the fluorine-containing cycloaliphatic polymer and using the circuit conductive layer made of the superconducting metal. That is, an adhesion strength is low between the insulating film made of the fluorine-containing polymer or the fluorine-containing cycloaliphatic polymer and the circuit conductive layer made of the superconducting metal, because functional groups composing the fluorine-containing polymer or the fluorine-containing cycloaliphatic polymer are bonded with atoms of the superconducting metal of the circuit conductive layer in a thermally unstable state. As a result, the multi-layered circuit substrate suffers a poor reliability.